Types[edit]
Labile kerogen breaks down to form heavy hydrocarbons (i.e. oils), refractory kerogen breaks down to form light hydrocarbons (i.e. gases), and inert kerogen forms graphite.
A Van Krevelen diagram is one example of classifying kerogens, where they tend to form groups when the ratios of hydrogen to carbon and oxygen to carbon are compared.[10]
Type I: Sapropelic[edit]
Type 1 oil shales yield larger amount of volatile or extractable compounds than other types upon pyrolysis. Hence, from the theoretical view, Type 1 kerogen oil shales provide the highest yield of oil and are the most promising deposits in terms of conventional oil retorting [11]
containing alginite, amorphous organic matter, cyanobacteria, freshwater algae, and land plant resins
Hydrogen:carbon ratio > 1.25
Oxygen:carbon ratio < 0.15
Shows great tendency to readily produce liquid hydrocarbons.
It derives principally from lacustrine algae and forms only in anoxic lakes and several other unusual marine environments
Has few cyclic or aromatic structures
Formed mainly from proteins and lipids
Type II: Planktonic[edit]
Type II kerogen is common in many oil shale deposits. It is based on marine organic materials, which are formed in reducing environments. Sulfur is found in substantial amounts in the associated bitumen and generally higher than the sulfur content of Type I or III. Although pyrolysis of Type II kerogen yields less oil than Type I, the amount acquired is still sufficient to consider Type II bearing rocks as potential oil sources
Plankton (marine)
Hydrogen:carbon ratio < 1.25
Oxygen:carbon ratio 0.03 to 0.18
Tend to produce a mix of gas and oil.
Several types:
Sporinite: formed from the casings of pollen and spores
Cutinite: formed from terrestrial plant cuticle
Resinite: formed from terrestrial plant resins and animal decomposition resins
Liptinite: formed from terrestrial plant lipids (hydrophobic molecules that are soluble in organic solvents) and marine algae
They all have great tendencies to produce petroleum and are all formed from lipids deposited under reducing conditions.
Type II: Sulfurous[edit]
Similar to Type II but high in sulfur.
Type III: Humic[edit]
Land plants (coastal)
Hydrogen:carbon ratio < 1
Oxygen:carbon ratio 0.03 to 0.3
Material is thick, resembling wood or coal.
Tends to produce coal and gas (Recent research has shown that type III kerogens can actually produce oil under extreme conditions) [12][citation needed]
Has very low hydrogen because of the extensive ring and aromatic systems
Kerogen Type III is formed from terrestrial plant matter that is lacking in lipids or waxy matter. It forms from cellulose, the carbohydrate polymer that forms the rigid structure of terrestrial plants, lignin, a non-carbohydrate polymer formed from phenyl-propane units that binds the strings of cellulose together, and terpenes and phenolic compounds in the plant. Type III kerogen involving rocks are found to be the least productive upon pyrolysis and probably the least favorable deposits for oil generation
Type IV: Residue[edit]
Hydrogen: carbon ratio < 0.5
Type IV kerogen contains mostly decomposed organic matter in the form of polycyclic aromatic hydrocarbons. They have no potential to produce hydrocarbons.[13]
Origin of material[edit]
Terrestrial[edit]
The type of material is difficult to determine but several apparent patterns have been noticed.
Ocean or lake material often meet kerogen type III or IV classifications.
Ocean or lake material deposited under anoxic conditions often form kerogens of type I or II.
Most higher land plants produce kerogens of type III or IV.
Some coal contains type II kerogen.